Majority of cancer-related deaths are caused by metastasis, a complex process initiated by spreading of tumor cells into circulation, where they are referred to as circulating tumor cells (CTCs). One of the limiting steps towards preventing or treating metastasis is our insufficient knowledge of the biological properties of CTCs, the population that contains metastatic precursors. We have previously developed a microfluidic device to isolate CTCs with high efficiency in human and mice. Our work on analyzing pancreatic CTCs have identified that MAP3K7, also called TGF- activated kinase (TAK1), plays an important role in promoting resistance to anoikis - apoptosis induced by detachment from the extracellular matrix, one of the features to facilitate CTCs to survive during transit to distant sites. In addition, our most recent research has demonstrated the evidence of epithelial-mesenchymal transition (EMT) in CTCs of metastatic breast cancer patients and associated signaling pathways, one of which is the well-known EMT inducing cytokine - TGF-. As a downstream target of TGF-,TAK1 may be involved in the EMT process thus warrant further investigation. My pilot analysis in Oncomine database indicated a significantly higher expression of TAK1 in breast cancers relative to other type of cancers, however, the role of TAK1 is not very well investigated in breast cancers. In preliminary experiments, I also found that breast cancer cells grown in suspension are exquisitely sensitive to TAK1 inhibition. All the prior work lead to the hypothesis that TAK1 may play an important role in promoting breast cancer metastasis. Whereas pancreatic cancer is often metastatic at the time of diagnosis, breast cancer follows a more prolonged course, where the ability to prevent blood borne metastasis may have real clinical application. Thus, the overall goal of the proposed experiments is to understand the TAK1 signaling pathways involved in breast cancer metastasis, including analyzing the features of anoikis resistance, EMT, and its importance in breast cancer metastatic mouse models. I will analyze the role of TAK1 on anoikis resistance in different subtypes of breast cancer cells by introducing different constructs of TAK1 that can either activate TAK1 or abolish TAK1 kinase function. In addition, I will examine the contribution of TAK1 in promoting EMT in breast cancer cells. Finally, I will evaluate the functional consequences of inhibiting TAK1, via a doxycycline-inducible suppression of TAK1, in CTCs and metastases formation in a xenograft breast cancer metastatic mouse model. Completing these goals will lead to a better understanding of this important kinase pathway and provide potential pre-clinical data on a targetable pathway for preventing breast cancer dissemination. The overall career development goal of the proposed work is to enable me to begin a productive, independent research career focusing on understanding the mechanisms of breast cancer metastasis.